Twin-shaft gas turbine

ABSTRACT

A twin-shaft gas turbine  1,  which has a gas generator  2  including a compressor  7,  a combustor  8,  and a high-pressure turbine  9,  is configured to make a first control mode and a second control mode selectively useable for control of the gas generator. In addition, in the first control mode, an IGV angle in the compressor is controlled in accordance with a corrected shaft rotation speed of the gas generator, and in the second control mode, the IGV angle is controlled to maintain a constant gas generator shaft rotation speed. Furthermore, the first control mode is used to start, to stop, and to operate the turbine under fixed or lower load conditions, and that the second control mode is used under operational states other than those to which the first control mode is applied.

This is a divisional application of U.S. application Ser. No.12/493,351, filed Jun. 29, 2009, the contents of which are herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to twin-shaft gas turbines, andmore particularly, to controlling a gas generator in a twin-shaft gasturbine.

2. Description of the Related Art

Generally, a twin-shaft gas turbine includes a gas generator constitutedby a compressor, a combustor, and a high-pressure turbine. This gasturbine also includes a low-pressure turbine (power turbine) connectedto a load, with a gas generator shaft (a rotary shaft of the gasgenerator) being separated from a rotary shaft of the low-pressureturbine. In the gas generator, the compressor generates compressed airand supplies the compressed air to the combustor in which a fuel mixedlywith the compressed air is then burned, thus combustion gases aregenerated. The combustion gases that have thus been produced by thecombustor rotationally drive the high-pressure turbine to generate adriving force of the compressor. After this, the combustion gases arefurther sent to the low-pressure turbine to drive it for rotation.

In such conventional twin-shaft gas generator, control that providesangle control of the compressor inlet guide vane (IGV), based on acorrected rotation speed of the gas generator shaft, that is, correctedrotation speed responsive IGV angle control has been totally applied asmost common gas-generator control, irrespective of an operational stateof the gas generator.

The disclosures given in JP-2007-40171-A, JP-08-82228-A, andJP-63-212725-A, for instance, are known as examples of a twin-shaft gasgenerator.

SUMMARY OF THE INVENTION

As discussed above, corrected rotation speed responsive IGV anglecontrol is conducted in the gas generator of the conventional twin-shaftgas generator specifications. In this case, as shown in FIG. 7A, the IGVangle changes according to the corrected rotation speed having acorrelation with respect to an atmospheric temperature. As shown in FIG.7B, therefore, lines of operation also change, which in turn changes thegas generator shaft rotation speed according to the atmospherictemperature. In addition, since positions on the lines of operationvary, the load or deterioration of the turbine further changes the gasgenerator shaft rotation speed.

These changes in the rotation speed of the gas generator shaft causeresonance problems. In other words, the changes in the rotation speed ofthe gas generator shaft make this shaft rotation speed more likely toapproach a resonance rotation speed. As the shaft rotation speedactually approaches the resonance rotation speed, resonance arises andshaft vibration increases. Such a resonance problem as this becomesparticularly serious during high-speed rotation under high loadoperating conditions, and the resonance under the high-speed rotationalstate enhances a possibility of damage to rotor blade of turbine orrotor blade of compressor. For these reasons, the control scheme thattotally applies corrected rotation speed responsive IGV angle controlhas required imparting a structure for avoiding the resonance at thespeed assumed, or imparting to rotor blade a structure that allows therotor blade to withstand the resonance, and consequently, costs haveincreased.

The present invention has been made with a backdrop of the abovecircumstances, and an object of the invention is to effectively resolveresonance problems in a twin-shaft gas turbine, associated with changesin a rotation speed of a gas generator shaft, and more particularly, aresonance problem under a high-speed rotational state of the gasgenerator shaft.

Corrected rotation speed responsive IGV angle control is effective foravoiding compressor surging. However, in the regions that the shaftrotation speed of the compressor, or the rotation speed of the gasgenerator shaft, reaches a constant value or more, the compressorincreases in stability and surging does not pose too serious a problem.Therefore, while corrected rotation speed responsive IGV angle controlis required under a low-speed rotational state of the gas generatorshaft, such IGV angle control is not always required during thehigh-speed rotational state of the gas generator shaft in the regionsthat the stability of the compressor is ensured. The resonance problem,on one hand, becomes serious during such high-speed rotation of the gasgenerator shaft as in the regions that compressor stability can beobtained.

Accordingly, corrected-speed responsive IGV angle control is applied tooperational states under which the gas generator shaft rotates at lowspeed (these operational states occur during operational starts, duringoperational stops, and during low load operation under fixed or lowerload conditions), whereas control for maintaining a constant gasgenerator shaft rotation speed, that is, shaft rotation speed constantIGV angle control is applied to an operational state under which the gasgenerator shaft rotates at high speed (i.e., high load operation).

Using appropriate one of different control modes for a particularoperational state in this way makes it possible to resolve the resonanceproblem effectively and to respond to compressor surging effectively.This means that during the gas generator shaft high-speed rotation thatrenders the resonance problem particularly serious, since shaft rotationspeed constant IGV angle control keeps the gas generator shaft rotationspeed constant, the situation where the gas generator shaft rotationspeed approaches the resonance rotation speed can be avoided effectivelyand the resonance problem can therefore be resolved effectively. In themeantime, compressor surging that becomes a problem during the low-speedrotation of the gas generator shaft can be avoided by using correctedrotation speed responsive IGV angle control.

The present invention solves the foregoing problem in line with theconcepts described above. More specifically, a twin-shaft gas turbinewith a gas generator including a compressor to generate compressed air,a combustor to generate combustion gases by burning a fuel mixedly withthe compressed air supplied from the compressor, and a high-pressureturbine rotationally driven by the combustion gases supplied from thecombustor, the high-pressure turbine being used to generate a drivingforce of the compressor, is configured described below. A first controlmode and a second control mode are selectively useable for control ofthe gas generator. In the first control mode, an IGV angle in thecompressor is controlled in accordance with a corrected shaft rotationspeed of the gas generator, and in the second control mode, the IGVangle is controlled to maintain a constant gas generator shaft rotationspeed. Furthermore, the first control mode is used to start, to stop,and to operate the turbine under fixed or lower load conditions, and thesecond control mode is used under operational states other than those towhich the first control mode is applied.

Under a state of high gas-generator shaft rotation speeds and small IGVangles, deterioration of performance due to a separated flow of air at ablade of the compressor is prone to occur, which, in turn, easily causesicing as well. It is preferable, therefore, that such situations be madeavoidable. For these reasons, in a preferred embodiment of suchtwin-shaft gas turbine of the present invention as outlined above, thegas turbine allows a third control mode to intervene during a modechange between the first control mode and the second control mode, andin the third control mode, a constant IGV angle is maintained withoutrelying upon the rotation speed of the gas generator shaft.

According to the present invention outlined above, the resonance problemarising under a high-speed rotational state of a gas generator shaft ina twin-shaft gas turbine can be resolved effectively. Effective responseto compressor surging can also be implemented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a twin-shaft gas turbineaccording to a first embodiment;

FIG. 2 is a diagram showing an IGV angle controller configuration in thefirst embodiment;

FIGS. 3A and 3B are diagrams that represent relationships of an IGVangle with respect to a corrected rotation speed and actual rotationspeed of a gas generator shaft in the first embodiment;

FIG. 4 is a diagram showing a configuration of a twin-shaft gas turbineaccording to a second embodiment;

FIG. 5 is a diagram showing an IGV angle controller configuration in thesecond embodiment;

FIGS. 6A and 6B are diagrams that represent relationships of an IGVangle with respect to a corrected rotation speed and actual rotationspeed of a gas generator shaft in the second embodiment; and

FIGS. 7A and 7B are diagrams that represent relationships of an IGVangle with respect to a corrected rotation speed and actual rotationspeed of a gas generator shaft in a conventional control technique.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereunder, embodiments of the present invention will be described. Atwin-shaft gas turbine 1 according to a first embodiment is shown inschematic form in FIG. 1. The twin-shaft gas turbine 1 includes a gasgenerator 2 and an output turbine 3.

The output turbine 3 includes a low-pressure turbine 4 and a load 5 asits major constituent elements, the load 5 being connected to thelow-pressure turbine 4 via an output turbine shaft 6 which also operatesas a rotor of the turbine 4.

The gas generator 2 includes a compressor 7, a combustor 8, ahigh-pressure turbine 9, and a gas generator control unit 10, as itsmajor constituent elements.

The compressor 7 generates compressed air by letting air in from theatmosphere and compressing this air. Also, the compressor 7 has an inletguide vane (IGV) 11 at its air inlet side. The IGV 11 is constructed tomake its opening angle changeable via an IGV driver 12, thus changing anair inlet rate of the compressor 7.

The combustor 8 generates combustion gases 17 by receiving a fuel 15from a fuel supply 13 via a fuel control valve 14 and burning the fuel15 mixedly with the compressed air 16 from the compressor 7.

The high-pressure turbine 9 adapted to transmit a driving force to thecompressor 7 via a gas generator shaft 18 which is also a rotor of theturbine 9 is rotationally driven by the combustion gases 17 from thecombustor 8 to generate the driving force. The combustion gases 17 thathave acted upon the rotational driving of the high-pressure turbine 9 todecrease in pressure are further sent therefrom to the low-pressureturbine 4 to drive it for rotation.

The gas generator control unit 10 includes a fuel controller 19 and anIGV angle controller 20.

The fuel controller 19 provides control of the fuel control valve 14,based upon data from a rotation speed detector 27 which detects arotation speed of the output turbine shaft 6, and upon load state dataobtained about the load 5. Thus, the fuel controller 19 controls thesupply of the fuel 15 from the fuel supply 13 to the combustor 8.

The IGV angle controller 20 controls the angle of the IGV 11 through thecontrol of the IGV driver 12. An example of an IGV angle controllerconfiguration is shown in FIG. 2. The IGV angle controller 20 in thisexample includes a first controller 21, a second controller 22, anoperational state discriminator 23, and a mode selector 24.

The first controller 21 executes control in a first control mode. In thefirst control mode, the first controller 21 conducts corrected rotationspeed responsive IGV angle control to adjust the IGV angle on the basisof the corrected rotation speed of the gas generator shaft 18. Thiscorrected rotation speed of the gas generator shaft 18 is obtained bynormalizing an actual rotation speed value thereof (this value is givenby a speed detector 25 that detects actual rotation speeds of the gasgenerator shaft 18) with an atmospheric temperature value (this value isgiven by a thermometer 26 that measures atmospheric temperatures). Morespecifically, the corrected rotation speed Nt is obtained using thefollowing expression, with the actual rotation speed being representedas N and the atmospheric temperature as T:

Nt=N−[288.15/(273.15+T)]^(1/2)

The second controller 22 executes control in a second control mode. Inthe second control mode, the second controller 22 conducts IGV angleadjustments by shaft rotation speed constant IGV angle control to obtaina constant gas generator shaft rotation speed. This constant rotationspeed by shaft rotation speed constant IGV angle control is a ratedrotation speed, for example.

The operational state discriminator 23 discriminates a particularoperational state on the basis of data such as the load data. Morespecifically, the operational state discriminator 23 discriminateswhether the operational state of the turbine is a first operationalstate (either a starting operational state, a stopping operationalstate, or a low load operational state) or a second operational state(an operational state other than the first operational state, i.e., ahigh load operational state). This discrimination process assumes thatIGV angle data on a stable operational region of the compressed air 16is used as a measure for the discrimination between the low loadoperational state and the high load operational state. That is to say,an appropriate target IGV angle for a stable operational regionaccording to particular characteristics of the compressed air 16 is setand whether the operational state is the low load operational state orthe high load operational state is discriminated on the basis of thetarget IGV angle.

The mode selector 24 selects a control mode appropriate fordiscrimination results in the operational state discriminator 23. Morespecifically, when the discriminated operational state is the firstoperational state, the first controller 21 is started, and when thediscriminated operational state is the second operational state, thesecond controller 22 is started. Briefly, the appropriate mode isselected so that corrected rotation speed responsive IGV angle control,that is, the first control mode, will be used for the first operationalstate, and so that shaft rotation speed constant IGV angle control, thatis, the second control mode, will be used for the second control mode.

As set forth above, the IGV angle controller 20 selectively uses thecorrected rotation speed responsive IGV angle control mode or the shaftrotation speed constant IGV angle control mode according to theparticular operational state. A relationship between the correctedrotation speed of the gas generator shaft 18 and IGV angle under suchcontrol by the IGV angle controller 20 is represented in FIG. 3A, and arelationship between the actual rotation speed of the gas generatorshaft 18 and the IGV angle, in FIG. 3B. As can be seen from thesegraphs, under low load conditions, lines of operation are the same,regardless of the atmospheric temperature, but under high loadconditions, the corrected rotation speed changes with the atmospherictemperature. Meanwhile, however, the lines of operation under the lowload conditions change with the atmospheric temperature, the rotationspeed of the gas generator shaft 18 becomes constant under the high loadconditions.

Use of such control allows effective resolution of the resonanceproblem, that is, effective reduction of an increased likelihood ofdamage to the turbine and/or the compressor due to the resonance arisingduring high-speed rotation of the gas generator shaft 18 when therotation speed approaches the resonance rotation speed. Such controlalso allows effective response to compressor surging during low-speedrotation. These advantages allow resonance-associated design loads to berelieved and costs to be reduced.

A second embodiment is described below. A configuration of a twin-shaftgas turbine 31 according to the second embodiment is shown in schematicform in FIG. 4. The twin-shaft gas turbine 31 of the present embodimentis substantially the same as the twin-shaft gas turbine 1 of FIG. 1,except that a gas generator control unit 10 of the turbine 31 includesan IGV angle controller 32 instead of the IGV angle controller 20 inFIG. 1. Configurational features and characteristics of the twin-shaftgas turbine 31, therefore, are mainly described below, with thedescription of the foregoing embodiment being invoked forconfigurational features and characteristics common to those of thetwin-shaft gas turbine 1.

The IGV angle controller 32, as its configuration is shown in FIG. 5,includes a third controller 33 in addition to substantially the samefirst controller 21, second controller 22, operational statediscriminator 23, and mode selector 24, as those of FIG. 2.

The third controller 33 executes control in a third control mode. In thethird control mode, the third controller 33 conducts IGV angle constanthold control to maintain a constant IGV angle, independently of therotation speed of the gas generator shaft 18. This third control mode ofthe third controller 33, that is, the IGV angle constant hold controlmode is used during a mode change between the first control mode and thesecond control mode. This means that when the operational statediscriminator 23 discriminates a shift in operational state between thefirst operational state and the second operational state, the thirdcontroller 33 will be started to execute the control in the IGV angleconstant hold control mode.

The relationship between the corrected rotation speed of the gasgenerator shaft 18 and IGV angle under the control of the IGV anglecontroller 32 is represented in FIG. 6A, and the relationship betweenthe actual rotation speed of the gas generator shaft 18 and the IGVangle, in FIG. 6B. As can be seen from these graphs, since the controlin the IGV angle constant hold control mode can also be conducted,decreases in IGV angle at high rotation speeds of the gas generatorshaft can be avoided. That is to say, under the state of highgas-generator shaft rotation speeds and small IGV angles, thedeterioration of performance due to the separated flow of air at theblade of the compressor 7 is prone to occur, which, in turn, easilycauses icing as well. Such situations can be effectively avoided bymaking the third control mode intervene during a mode change between thefirst control mode and the second control mode. Reliability can also beimproved.

While embodiments of the present invention have been described above,these embodiments are only typical examples and the invention can beembodied in various forms without departing from the scope of theinvention.

1. A twin-shaft gas turbine with a gas generator, the gas turbinecomprising: a compressor having an inlet guide vane at its air inletside; a combustor for generating combustion gases by burning a fuelmixedly with the compressed air supplied from the compressor; and ahigh-pressure turbine rotationally driven by the combustion gasessupplied from the combustor, the high-pressure turbine being used togenerate a driving force of the compressor; wherein the gas turbinefurther comprises control means of the inlet guide vane; and the controlmeans of the inlet guide vane includes, a first control mode in which anopening angle of the inlet guide vane is controlled on the basis of acorrected rotation speed corresponding to atmospheric temperature of thegas generator shaft which rotates at low speed, a second control mode inwhich the opening angle of the inlet guide vane is controlled tomaintain a constant rotation speed of the gas generator shaft whichrotates at high speed.
 2. A twin-shaft gas turbine with a gas generator,the gas turbine comprising: a compressor having an inlet guide vane atits air inlet side; a combustor for generating combustion gases byburning a fuel mixedly with the compressed air supplied from thecompressor; and a high-pressure turbine rotationally driven by thecombustion gases supplied from the combustor, the high-pressure turbinebeing used to generate a driving force of the compressor; wherein thegas turbine further comprises control means of the inlet guide vane; andthe control means of the inlet guide vane includes, a first control modein which an opening angle of the inlet guide vane is controlled to avoidsurging of the compressor when the gas generator shaft which rotates atlow speed, a second control mode in which the opening angle of the inletguide vane is controlled to avoid the resonance of the compressor whenthe gas generator shaft which rotates at high speed.
 3. The twin-shaftgas turbine according to claim 1, wherein the gas turbine furthercomprises control means of the inlet guide vane; and the control meansof the inlet guide vane includes, a third control mode for maintaining aconstant angle of the inlet guide vane of the compressor independentlyof a rotation speed of the gas generator shaft is executed during a modechange between the first control mode and the second control mode. 4.The twin-shaft gas turbine according to claim 2, wherein the gas turbinefurther comprises control means of the inlet guide vane; and the controlmeans of the inlet guide vane includes, a third control mode formaintaining a constant angle of the inlet guide vane of the compressorindependently of a rotation speed of the gas generator shaft is executedduring a mode change between the first control mode and the secondcontrol mode.
 5. A control unit for a twin-shaft gas turbine with a gasgenerator, the gas turbine comprising: a compressor having an inletguide vane at its air inlet side; a combustor for generating combustiongases by burning a fuel mixedly with the compressed air supplied fromthe compressor; and a high-pressure turbine rotationally driven by thecombustion gases supplied from the combustor, the high-pressure turbinebeing used to generate a driving force of the compressor; wherein thecontrol unit includes, a first control mode in which an opening angle ofthe inlet guide vane is controlled on the basis of a corrected rotationspeed corresponding to atmospheric temperature of the gas generatorshaft which rotates at low speed, a second control mode in which theopening angle of the inlet guide vane is controlled to maintain aconstant rotation speed of the gas generator shaft which rotates at highspeed.
 6. A method for controlling operation of a twin-shaft gas turbinewith a gas generator, the gas turbine comprising: a compressor having aninlet guide vane at its air inlet side; a combustor for generatingcombustion gases by burning a fuel mixedly with the compressed airsupplied from the compressor; and a high-pressure turbine rotationallydriven by the combustion gases supplied from the combustor, thehigh-pressure turbine being used to generate a driving force of thecompressor; wherein the method includes, controlling the opening angleof the inlet guide vane on the basis of a corrected rotation speedcorresponding to atmospheric temperature of the gas generator shaftwhich rotates at low speed, controlling the opening angle of the inletguide vane to maintain a constant rotation speed of the gas generatorshaft which rotates at high speed.